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Residential peak demand questions

Calum_Wilde | Posted in General Questions on

I’m sure most of us have read Dana Dorsett’s comments on residential peak demand based pricing that is gaining interest from utilities across North America. Those comments always come up in other members comments so while I feel like I have several comments and questions I try not to derail another persons thread too much. I was hoping to start a thread about that subject so I could ask those questions.

My first question is easy to ask, probably not so easy to answer. How much should we home owners be paying attention to our peak demand? Not just from a potential pricing/billing standpoint, but from a green standpoint? I figure that if utilities are paying large enough amounts of money to mitigate those peaks that they’re looking for ways to move that cost to the customer, than they’re likely using more expensive plants to generate that power. And those more expensive plants likely spew out more pollution…? So, basically, should we be expending time and/or money to reduce our peak loads in an effort to make the grid more green?

I have several possible methods in mind that may or may not be beneficial, but I’ll leave that for after I read any replies this might get.

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Replies

  1. Jon_R | | #1

    Your peak demand matters very little. But your peak demand combined with many others that occur at the same time matters quite a bit. For example, consider the grid design needed to support every house's heat pump and tank water heater turning on after an extended power outage (assuming the typical case of no granular utility control of these).

  2. GBA Editor
    Martin Holladay | | #2

    Calum,
    In general, with few exceptions, peak demand is a concern of utility officials, not homeowners. The exception (as Dana Dorsett has told us) concerns tankless electric water heaters. Even if a homeowner can afford the cost of the electricity required for a tankless electric water heater under current rate structures, Dana warns readers that future changes in rate structures may make this type of water heater expensive to operate.

    Time-of-use billing is coming to many regions of the country, especially areas of California. The easiest way to take advantage of time-of-use billing is to do your laundry or wash your dishes during off-peak hours. If you have an electric car, and your have time-of-use billing, it makes sense to recharge your car during off-peak hours.

    The cost of batteries is still too high to justify their installation under current rate structures, but it's possible to imagine that, in a few short years, batteries will be cheap enough, and time-of-use billing structures compelling enough, for homeowners to justify the installation of a battery (along with a controller that is smart enough to take advantage of future economic opportunities to buy and sell power). But we're not there yet.

  3. Northernbuilt | | #3

    My local rural electric cooperative has done a very good job selling off-peak control programs. They've managed to move their peak to the middle of the night, except during the summer, by controlling electric water and space heating. Even though we are in a northern climate (northern Minnesota), air conditioning has a big effect on the peak, some years even more than heating during the winter. The REC does offer a cycled air conditioning program, but few people use the program.

  4. Calum_Wilde | | #4

    Randy,

    What products do they use to make that possible? How does that effect your daily life?

  5. Calum_Wilde | | #5

    JON,

    Yes, this is clearly something that any one person isn't going to fix. It would take a collective effort from many people, but that will never happen if someone doesn't start it. My question isn't whether I can fix this by myself, but would it make a difference to our environment if many people started looking into this?

  6. Calum_Wilde | | #6

    Martin,

    Time of use billing is a stop gap effort at best to more granular control.

    I'm aware that peak demand is a concern for utility officials. I'm wondering if their present mitigation strategies are causing undue amount of pollution, and if it would be a better for the environment to mitigate those peaks at the demand end.

    I also think there's several ways for homeowners to mitigate demand peaks that aren't being explored/promoted presently. Or atleast, I haven't seen anything about them in my searches.

  7. GBA Editor
    Martin Holladay | | #7

    Calum,
    Utilities have employed demand response programs for years -- offered to either commercial or residential customers, depending on the utility. These programs aren't available everywhere, of course.

    Programs often involve installing controls that allow the remote control of air conditioners or water heaters. Utilities shut off these appliances during peak hours, in exchange for some type of incentive.

    If you want a do-it-yourself approach, do some research to determine peak demand hours in your location. You could, as a volunteer green crusader, install a timer on your water heater and your air conditioner if you wanted, and program the timers to disable these appliances during peak demand hours.

  8. Northernbuilt | | #8

    Calum,
    My electrical coop uses several load control programs that are either direct or sub-metered and controlled by radio frequency. The devices are controlled depending on the program. For example, electric water heating has 2 different programs, off-peak water heating is heated only overnight and requires a minimum of 100 gallon tank, usually a Marathon. A second program they call interruptible water heating is typically only turned off during peak times, usually from 6-9 am and again at 4-9 pm. Only required a 50 gal tank for that program. The typical family doesn't run out of hot water. Storage heat is another program, simular to off peak water heating, a forced air or hydronic electric storage furnace is "charged" over night and the heat is released during the day. A small company in North Dakota called Steffes manufactures the brick lined furnaces. The electric rate for this program is $.0495 per KW, very competative with natural gas. Other area utility companies will use what is called a power line carrier to control the electrical devices. A signal is sent over the power lines. We've been using these technologies for around 30 years. It's rare we even know when the devices are being controlled.

  9. Calum_Wilde | | #9

    Martin,

    From what I've seen there's two methods used to control residential peak demand, turn things off via a very course timing, or turn things off via a central control from the utility. Both of those seem horribly inadequate and antiquated.

    We have digital controllers for room heat that will only supply what the room needs and will maintain the temperature within a few tenths of a degree. I think something like that could be used for water heaters so they aren't spiking to 3kW-4.5kW just to maintain standby temperature.

    We could put a lower wattage heating element in water heaters, in the lower position only. That way low volume uses wont cause as much of a spike on the local grid, but higher volume uses that would normally trigger the upper element would still get similar recovery rate to what we're all expecting.

    For homes with electric stoves: Home owners could set the setpoint of their heating and/or AC so that it doesn't come on while the home owner is cooking. This could be as simple as a 3 or 4 deg F setback for an hour or two during the time that they typically cook. Even a right sized heatpump shouldn't struggle to get back to the desired temperature after such a short setback, but it would prevent two of the highest draw items in a house from operating at the same time. How that would be different than most water heater timers is that most heat pumps have much more flexible timers that can be varied on different days, and it would only cost the homeowner the time to set the timers. The same method could be deployed for any other predictable time of day that the homeowner is using other high draw items.

    Of course dishwashers and washers & dryers can be run outside of actual peak usage times. That's not new, but if things like this were promoted better it might get enough homeowners on board to avoid the roll out of mandatory time of use rates, which can be highly restrictive. Here in Nova Scotia we can opt into time of use rates, but the "peak time" doesn't end until 11pm. I have young children that need to shower at night, laundry that needs to get done throughout the week, and I'd really rather not fall asleep to the dulcet tones of my dishwasher. Like most areas we have a utility run efficiency program, but it only focuses on reducing overall usage. Maybe it's time we start looking at reducing peak demand as well as overall demand at a level that is attainable and understandable to the average homeowner. Installing storage is great, but it's prohibitively expensive (as you're well aware), and the infrastructure for utility run controls is expensive and causes concerns of privacy. The exceptionally basic controls of most water heater timers are offensively low tech in today's world, most don't even use solid state relays. The power required to keep the rely open during peak times is likely more than the power my water heater uses in standby over the same time period.

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